.\"	$OpenBSD: gio.4,v 1.6 2012/04/18 18:01:56 miod Exp $
.\"	$NetBSD: gio.4,v 1.20 2008/04/30 13:10:56 martin Exp $
.\"
.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" This document is derived from work contributed to The NetBSD Foundation
.\" by Antti Kantee.
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.Dd $Mdocdate: April 18 2012 $
.Dt GIO 4 sgi
.Os
.Sh NAME
.Nm gio
.Nd Graphics I/O GIO bus
.Sh SYNOPSIS
.Cd "gio0 at imc0"
.Sh DESCRIPTION
The
.Nm
bus is a bus for connecting high-speed peripherals to the main memory and
CPU.
The devices themselves are typically (but not necessarily) connected to the
.Xr hpc 4
peripheral controller, and memory and CPU are accessed through the
.Xr imc 4
system controller.
The
.Nm
bus is found on the Indigo, Indy, Challenge S,
Challenge M, and Indigo2 machines and exists in three incarnations:
GIO32, GIO32-bis, and GIO64.
.Pp
The devices currently supported under
.Ox
are:
.Pp
.Bl -tag -width 10n -compact -offset indent
.\" .It Xr giopci 4
.\" GIO-PCI bridge
.It Xr grtwo 4
SGI Express graphics
.It Xr hpc 4
SGI High performance Peripheral Controller
.It Xr impact 4
SGI Impact (aka Mardigras) graphics
.It Xr light 4
SGI Light graphics
.It Xr newport 4
SGI Newport graphics
.El
.Sh SEE ALSO
.Xr imc 4 ,
.Xr intro 4
.Sh CAVEATS
Challenge S systems may use only one
.Nm
DMA-capable expansion card, despite having two slots.
Cards based on the
.Xr hpc 4
controller, such as the GIO32 SCSI and E++ Ethernet adapters, must be
placed in slot 1 (closest to the side of the case).
All other cards must be placed in slot 0 (adjacent to the memory banks).
.Pp
Indigo2 and Challenge M systems contain either three or four GIO64 connectors,
depending on the model.
However, in both cases only two electrically distinct slots are present.
Therefore, distinct expansion cards may not share physical connectors
associated with the same slot.
On the other hand, these apparently redundant slot connectors allow
multiple board assemblies to draw more power from the bus, and also
helps mix
.Nm
and EISA boards in the same chassis.
In all systems, the upper two GIO64 connectors are GIO slot 1, while
the lower connectors (either one or two of them) are GIO slot 0.
